Composite piezoelectric transducers are recognized for their improved performance characteristics in acoustic and ultrasonic applications that require wide bandwidth and high sensitivity. In particular, composite transducer technology can provide significantly higher effective piezoelectric material coefficients than are available in conventional piezoceramic materials. Inherent advantages associated with composite transducer devices include lower acoustical impedence and higher coupling efficiency in the sound propagation medium, specifically, in water, air, and other gaseous media.
One form of piezoelectric composite transducer consists of piezoelectric rods, tubes, or rectangular bars oriented parallel to one another but spaced apart so as to be surrounded and bounded together by an epoxy matrix filler. This composite arrangement may be formed in the shape of a square or rectangular plate or a circular disk whose sound-radiating face is the surface of the plate or disk. The embedded piezoceramic elements are oriented perpendicular to the sound radiating face.
Another form of composite piezoelectric transducer is comprised of piezoceramic plates having a rectangular shape arranged parallel to one another but separated by epoxy bonding layers. This laminated composite array of piezoceramic plates and epoxy layers forms a square or rectangular plate whose sound-radiating face is the surface of the plate. The edges of the piezoceramic plates are oriented perpendicular to the sound-radiating face.
In the first described composite transducer, the cross-axis polarization piezoelectric coefficients of the piezoceramic material govern the acoustical operation. The piezoceramic rods are usually polarized along their length axis (oriented perpendicular to the radiating face). Improved performance characteristics are achieved by the lateral volume expansion and contraction of the piezoceramic elements acting on the surrounding epoxy matrix, giving rise to displacements and sound radiation normal to the face.
In the second described composite transducer, the plates are usually polarized in their thickness dimension (oriented parallel to the radiating face). Their parallel polarization piezoelectric coefficient governs the acoustical operation by applying lateral volume expansion and contraction to the surrounding epoxy matrix. This results in displacements and sound radiation normal to the face of the plate.